High current vacuum gap devices with slotted electrode vanes



March 11, 1969 J. M. LAF FERTY 3,432,

HIGH CURRENT VACUUM GAP DEVICES WITH SLOTTED ELECTRODE VANES I Filed May19, 1967 Sheet ofS / III I dd mes M Ldffer'ty, by GE His At tor'ney.

HIGH CURRENT VACUUM GAP DEVICES WITH SLOTTED ELECTRODE VANES Sheet FiledMay 19, 1967 PULSE Fig. 4.

v fl 4 4 .m M M 2 WNW e J L? m a 4 6 L o 2 \4 J t mm m 4 e fu t a me A 4i W m w 4 m x PULSE sou/e01:

SOURCE March 11, 1969 J. M. LAFFERTY 3,432,713

HIGH CURRENT VACUUM GAP DEVICES WITH SLOTTED ELECTRODE VANES Sheet FiledMay 19, 1967 Fig. 7.

I In venor-ndd mes MLdfv eri' ,& /05

(F ldis Attorney.

United States Patent 3,432,713 HIGH CURRENT VACUUM GAP DEVICES WITHSLOTTED ELECTRODE VANES James M. Latferty, Schenectady, N.Y., assignorto General Electric Company, a corporation of New YorkContinuation-impart of application Ser. No. 586,751,

Oct. 14, 1966. This application May 19, 1967, Ser. No. 639,844

US. Cl. 313231 12 Claims Int. Cl. H01j 17/26, 61/28 ABSTRACT OF THEDISCLOSURE Vacuum gap devices adapted for very high current usageinclude a first inner electrode having outwardly disposed thin vanes anda second outer electrode having inwardly disposed thin vanes. Vanes ofinner electrode are slotted to define a folded-back path of currentconduction therein. Folded-back current path causes flux lines causedthereby to move arcing paths within interelectrode gaps to large matingvane area and permit high currents to pass between electrodes withouthigh current density at any given point, thus avoiding anode spotformation.

This application is a continuation-in-part of my copending applicationSer. No. 586,751, filed Oct. 14, 1966, now Patent No. 3,356,894 which isa continuation-in-part of my copending application Ser. No. 535,948,filed Mar. 21, 1966, now Patent No. 3,356,893, both of which areassigned to the assignee of the present invention, the completespecifications of both of which are incorporated herein by referencethereto.

The present invention relates to improved high power, high currentvacuum gap devices, particularly those of the triggered vacuum gap andvacuum switch types, suitable for the attainment of very high power andcurrent ratings without the development of anode spots and the attendantdestructive erosion thereof. 7

Vacuum gap devices, in particlar vacuum switches and fixed vacuum gapsof the triggered vacuum gap type, have recently been the subject ofintense technological and commercial interest. After nearly 40 years ofdevelopmental evolution, commercial vacuum switches at high powerratings are presently being manufactured. Similarly, since the advent ofthe triggered vacuum gap disclosed and claimed in my US. Patent No.3,087,092, issued Apr. 29, 1963, and entitled Gas Generating SwitchingTube, gaps of this type which avoid the previously existing problems ofinstabilities and nonuniform breakdown voltages have been adapted for anumber of commercial applications. Both vacuum switches and triggeredvacuum gaps are often limited in their ability to operate at high powerlevels and, particularly, to carry currents of the hundreds of thousandsof ampere range for more than one half cycle, by the inability ofconventional anodes to withstand destructive melting caused by theformation of intense anode spots which are the anode footpoints ofindividual electric arcs existing between cathode and anode. In gapswit-h closely spaced electrodes, the destructive melting also occurs atthe cathode electrode, because of intense radiation and heating from theanode spots.

In my copending applications, Ser. No. 535,948, and 586,751, I disclosea novel arrangement of arc-electrodes for vacuum gap and vacuum switchdevices wherein the primary arc-electrodes include a first primary,central arcelectrode having a plurality of thin outwardly-dependingvanes which are interleaved with the inwardly-depending vanes of asecond primary, outer arc-electrode which is generally disposedoutwardly of said first electrode surrounding the same. By virtue ofthis arrangement, a plurality of arcing paths is provided and a highcurrent ca- 3,432,713 Patented Mar. 11, 1969 Accordingly, it is anobject of the present invention to 7 provide improved vacuum gap devicesby provision of a unique adaptation of the thin-vane, interleavedarc-electrode configuration which avoids the formation of anode spotsaltogether.

A further object of the present invention is to provide vacuum gapdevices, including vacuum switches and fixed gap devices which areadapted to operate at high current and power levels for long duty cycleswithout the formation of anode spots and thereby exhibit long-lifetimecharacteristics.

A further object of the present invention is to provide improvedtriggerable vacuum gap devices suitable for operation at higher currentsand higher voltage levels than heretofore obtainable, without theincidence of anode spots.

Yet another obejct of the present invention is to provide improved highcurrent, high power vacuum switches which may be utilized for a greaternumber of circuit interruptions than heretofore obtainable without theoccurrence of anode spots therein and the ultimate destruction of theelectrodes thereof.

In accord with one feature of the present invention, I provide a vacuumgap device including, as essential elements thereof, a pair of primaryelectrodes which may define therebetween a plurality of parallel vacuumgaps. More specifically, in accord with the present invention theelectrodes of the primary gap are interleaved between one another andcontained within an evacuable envelope which, during arcing issubstantially filled with an electron-ion plasma, which provides aninfinite number of current carrying paths, none of which has sufficientcurrent density to cause destructive melting of either anode or cathodeelectrodes and, specifically, of the anode electrode. In the embodimentof the invention one primary electrode constitutes a plurality ofoutwardly depending radial fins attached at the center thereof to acenterpost and the other primary arc-electrode comprises a plurality ofinwardly depending radial fins interleaved between the outwardlydepending radial fins and connected to the outward edges thereoftogether so as to form an electrically unitary electrode structure.

In all embodiments of the present invention, improved current carryingcharacteristics are obtained and anode spot formation is completelyeliminated by providing, in either the outwardly depending vanes of theinner primary arc-electrodes, or the inwardly-depending vanes of theouter arc-electrode, a pattern of slots which separate adjacent portionsof each vane so as to provide a foldedback path of current therein undercurrent carrying conditions. The folded-back current path causes fluxlines resulting from the current existing within each vane to interactwith electric current flow in the interelectrode gap to spread the pathsof current flow over a large electrode surface and inhibit any tendencyof the current carrying paths therebetween to bunch up at any given spotto cause a high current density and a resultant anode spot.

In one general class of embodiments of my invention the electrodestructure, as described hereinbefore, is permanently juxtaposed so as todefine a plurality of fixed gaps and current is initiated between thetwo primary electrode structures by the pulsing of a trigger apparatusassociated therewith to cause the injection into the primary gap of acharged electron-ion plasma to cause the breakdown thereof.

In accord with yet another general class of devices constructed inaccord with the present invention, the electrode structure, as describedhereinbefore, has one movable with respect to the other so that thecentral electrode apparatus, for example, may be moved with respect tothe outer electrode apparatus, either by a longitudinal motion or byrotation thereof. In this case, plasma to form a conduction path betweenthe primary arc-electrode is produced by the arc struck upon circuitinterrupting and the vaporizing and ionization of electrode material.The initial arc is struck upon a separation of the two electrodeapparatus and the are rapidly diffuses over the many parallel surfacesof the electrode structures so that the evacuated volume containing theelectrode is rapidly filled with an electron-ion plasma which conductshigh currents at high power levels until the occurrence of a currentzero, at which time the discharge is extinguished.

The novel features believed characteristic of the present invention areset forth in the appended claims. The invention itself, however,together with further objects and advantages thereof may be more readilyunderstood by reference to the appended drawing in which:

FIGURE 1 is a vertical cross sectional view with parts broken away of afixed gap triggerable vacuum device constructed in accord with thepresent invention,

FIGURE 2 is a perspective view of the inner electrode assembly of thedevice of FIGURE 1,

FIGURE 3 is a vertical cross sectional view with parts broken away of avariable gap vacuum switch constructed in accord with another embodimentof the present invention,

FIGURE 4 is a vertical cross sectional view, with parts broken away, ofyet another device constructed in accord with a further embodiment ofthe present invention,

FIGURES 5, 6, 7, 8, and 9 represent alternative structures to the lowercentral electrode assembly of the device illustrated in FIGURE 2 of thedrawing, and

FIGURE 10 is a vertical cross sectional view, with parts broken away, ofa device constructed in still another alternative embodiment of thepresent invention.

A triggered vacuum gap constructed in accord with one embodiment of theinvention and illustrated in FIG- URE 1 of the drawing comprises anevacuable envelope 1 containing therein a pair of primary electrodeassemblies including a central electrode assembly 2 and an outerelectrode assembly 3. Central electrode assembly 2, comprises aplurality of outwardly-depending radial vanes 4, each of which is thin,having a small thickness dimension as compared with its length and widthdimensions, and is substantially perpendicular to a transverse plane,and which are fastened at the lowest ends to a plate or disc 5 which isconnected to and supported upon an electrode support member 6.

Electrode assembly 2 is also illustrated in FIGURE 2 of the drawing inperspective, showing the inter-relationship of vanes 4, plate 5, andsupport member 6.

Returning to FIGURE 1, outer electrode assembly 3 comprises a hollow,cylindrical member 7 and a plurality of inwardly depending radial vanes8 physically and electrically connected thereto. Vanes 8 are also thin,having a small thickness dimension as compared with their length andwidth dimensions and substantially perpendicular to the same traverseplane. Electrode assemblies 2 and 3 are juxtaposed so that theindividual, inwardlydepending vanes 8 and the individual,outwardly-depending vanes 4 define a plurality of electrically parallelbreakdown gaps therebetween. Each of the electrically parallel gaps issubstantially of equal dimension to the others. Vanes 8 of arc-electrodeassembly 3 extend for substantially the entire length of the dischargespace within envelope 1. The vanes 4 of arc-electrode assembly 2 aresomewhat shorter as is consistent with the necessity of maintaining thespace between arc-electrodes 2 and apertured end wall members 9 and 10of such length to prevent a spurious arcing, since members 9 and 10 areof the same electrical potential as arc-electrode 3. As a practicalmatter, however, vanes 4 are at least one-half of the length of vanes 8.The thinness of vanes 4 and 8 is such that essentially no appreciableincrease in electrical resistivity is incurred, but due to the thinness,a large number of parallel primary breakdown gaps, none of which isoverloaded by extreme current densities, may be formed in a relativelysmall volume.

In further accord with the invention, each of vanes 4 of arc-electrodeassembly 2 is slotted, horizontally at slot 11 at a distance that is atleast approximately twothirds of the length of the vanes 4 from the endthereof at which breakdown first occurs. Vertical slot 12 intersectshorizontal slot 11 and is located at a region at least approximatelytwo-thirds of the width of vane 4 to the center post. The function ofslots 1 and 12 in vane 4 of arc-electrode assembly 2 is to provide afolded-back path for current flow within vane 4. Thus, for example, anypath of current conduction from vanes 8 of electrode assembly 3 to aportion of vane 4 of arc-electrode assembly 4 causes a current pathwhich passes upwardly over the upper tip of slot 12 and downwardly alongthe center post causing a folded-back current conduction path. Thisfolded-back current conduction path causes the flux lines of themagnetic field caused thereby to reinforce the magnetic field caused bycurrent paths within the external arc-electrode 3, to force the paths ofcurrent conduction radially outwardly from the point of initialbreakdown adjacent the source of electron-ion plasma injected into theinterelectrode space and upwardly along the large areas of vanes 4 and8. This precludes the bunching up of conduction paths at the corner ofthin vanes 4 of arcelectrode 2 and the establishment of high densityanode spots thereat, which can cause erosion, damage and subsequentfailure of the device 1.

Envelope 1 of the device of FIGURE 1 contains a metallic, substantiallycylindrical sidewall member 7 and a pair of oppositely disposed end caps9 and 10, respectively. Both sidewall and end wall members are composedof a suitable conductive material, as for example high purity cooper, orthe equivalent. The cylindrical sidewall member may be the cylindricalportion 7 of exterior electrode assembly, as illustrated, or,alternatively the electrode assembly may be firmly mechanically andelectrically connected to the interior thereof. The aperture in upperend wall member 9 is hermetically closed with a suitable triggerelectrode assembly 13 having a trigger anode 14, a trigger cathode 15,and a trigger gap therein (not shown) for supplying a pulse of gaseousion-electron plasma or vaporized and ionized electrode material to causebreakdown between primary electrode assemblies 2 and 3 upon theinitiation of a suitable electrical signal to trigger electrode assembly13. Electrode assembly 13 is suitably brazed to end plate 9. Suitabletrigger electrode assemblies are illustrated, disclosed and claimed inmy aforementioned US. Patent and in my copending applications, Ser. No.516,914, Ser. No. 516,942; and Ser. No. 516,943, all filed Dec. 28, 1965and assigned to the assignee of the present invention.

The trigger electrode assembly 13 is surrounded by a conductivecylindrical member 16 which is brazed to end plate 9 and which may be anintermediate electrical connection therebetween and electrical terminalconductor 17. An insulated trigger electrode lead 18 passes throughcylinder 16 to allow for connection of trigger electrode assembly 13 toa suitable source of pulsed voltage (not shown).

Central electrode support rod 6 passes down through aperture 20 in endwall member 10, through a ferruled breakdown shield 21 and is supportedby a closure disc 22 which is hermetically sealed to a ceramic insulatorbushing 23, which in turn is hermetically sealed to end closure by meansof a suitable annular chrome-iron or equivalent alloy sealing flange 24.A central tubulation in support rod 6 permits the evaculation ofenvelope 1 and is sealed into an exterior tubulation 26 which extendsthrough the end of support rod 6 and is pinched off at 27 to completethe evacuation and sealing of envelope 1.

FIGURE 3 of the drawing illustrates in vertical cross section with partsbroken away, another embodiment of the invention. In FIG. 3, which hasmany similar structural features common to the embodiment of FIGURE 1,like numerals are utilized to identify like members. In F IG- URE 3, anevacuable envelope 1 comprises a general cylindrical metallic sidewallmember and a pair of upper and lower end wall members 9 and 10,respectively. The aperture in end plate 10 is closed by an hermetic sealbetween an annular sealing flange member 28 of a suitable Fe-Ni- Coalloy, or equivalent, and a ceramic insulating bushing 29. Ceramicinsulating bushing 29 is closed by an annular apertured end plate 30which is hermetically sealed by ceramic-to-metal sealing techniquesthereto and welded, brazed, or otherwise suitably fastened to alongitudinally flexible bellows 31 which is capped by an annular endpiece 32 which is sealed around and, by an hermetic seal, sealed toelectrode support member 6 to complete a vacuum-tight envelope. Withinthe envelope of FIGURE 3, a first central primary electrode assembly 2comprising a plurality of slotted outwardly-depending, radial vanes 4 isinterdigitated between the inwardly-depending radial vanes 8 of an outerelectrode assembly 3 which is substantially the same as that illustratedin the embodiment of FIGURE 1 of the drawing and which is electricallyand mechanically a portion of the outer electrode assembly 3. Vanes 4and 8 are thin, as described hereinbefore, define a plurality ofelectrically-parallel gaps and are substantially perpendicular to thesame transverse plane. As mentioned hereinbefore, vanes 4 are slottedwith horizontal and vertical slots 11 and 12, as in the embodiment ofFIGURE 1 and illustrated more particularly in FIGURE 2 of the drawing,in order to cause current conduction therethrough to be folded-back tocause the interaction of the magnetic fields with the conduction currentpaths to force conduction current paths outwardly from the center ofenvelope 1, downwardly along the surface of vanes 4 and 8 in order toprevent the concentration of conduction paths at any given point,primarily the corner of vanes 4 by electromagnetic bunching and theestablishment of a destructive anode spot upon the periphery of vane 4to cause erosion and melting thereof. Additionally, due to the method ofinitiating herein, vanes 4 are attached to support member 6 only at theupper portion thereof to provide a doubly foldedback current path.

A metallic contact ring 33 rests in electrical and mechanical contactwith the inner surface of the lower metallic end plate 10, and is also,electrically, a portion of electrode assembly 3.

As in the embodiment of FIGURE 1, the device of FIGURE 3 may beevacuated to a central tubulation in electrode support member 6 whichterminates in a tubulation which, after evacuation, is sealed to vacuumby a pinch. The device of FIGURE 3 constitutes a vacuum switch orcircuit interrupter. In operation, the two primary electrode assemblies2 and 3 are brought into electrical circuit-making position by adownward thrust upon annular flange 34 surrounding the lower end ofelectrode support member 6 or an equivalent force supplied by means notillustrated. At the end of the downward stroke, the lower end edges ofthe outwardly depending radial vanes 4 of central electrode apparatus 2impinge upon, and make electrical contact with, annular contact ring 33.While any number of contact vanes may be used, contact at all pointsbetween vanes 4 and ring 33 is facilitated if only three vanes extendfrom the central post. A circuit to be switched is connected through theswitch in series circuit relationship therewith by making one deviceterminal to the lower end of electrode support member 6, as representedby arrow A. The other terminal may be made at suitable connecting studsattached to the outward portion of lower end plate 10, contact studsbeing represented by arrows B. Between these terminals, a source ofalternating voltage may be connected in series circuit relationship withan electric load to be switched.

To interrupt the fiow of current through the switch, the electrodesupport member 6 is moved longitudinally upward, as permitted by bellows31, separating the lower portions of vanes 4 of electrode assembly 2from the upper surface of contact ring 33. A plurality of arcs arethereby struck between each of the vanes and the contact ring. Since thepath of current through support member 6, electrode assembly 2, the arc,contact ring 33, lower end plate 10, and a plurality of peripheralterminal lugs at B constitutes a loop, magnetic forces cause aconcentration of flux at the center of the loop which urges the arcupwardly between the vanes of the inwardly depending outer electrodeassembly and the outwardly depending, inward electrode assembly, thustending to render the entire surface of the vanes available as contactsurfaces on the electric arc. To reinforce this force tending to causethe entire surface of vanes 4 and 8 of arc-electrode assemblies 2 and 3to be active arcing surfaces in operation, slots 11 and 12 cause thepath of current within vanes 4 of arc-electrode assembly 2 to befolded-back upon itself. This causes a further reinforcement of themagnetic field to act in conjunction with the current paths across theinterelectrode gap, to cause any tendency of the current paths to bunchat the corners of the vanes 4 of arc-electrode 2 to eliminated andforces the conduction paths upwardly along the entire surface of vanes 4of arc-electrode assembly 2.

The location of electrical terminals for current connection as shown inFIGURE 3 is extremely important. While it has long been recognized thatdispersal of high current carrying arcs into a plurality of segments,both in series and parallel, is desired in arcing devices, theachievement of such dispersal has not heretofore been effectivelyobtained. Any system in which the initial arc is struck between one pairof electrodes and transferred to another pair is difficult to achievebecause the arc always seeks the lowest energy position. Herein,magnetic forces generated by the arc itself are utilized in a novelfashion to force the are into the space between the interleaved radialvanes and, by virtue of slots 11 and 12, to force the conduction pathsbetween the vanes of the two arcelectrode assemblies to spread upwardlyalong the entire surface of vanes 4 and 8. If, on the other hand,terminals were placed longitudinally along the axis of the device ofFIGURE 1 and attempts were made to utilize the vanes, the balancedmagnetic fields established by the initial arcs struck between vanes 4and ring 33 would prevent the original arc or arcs from ever beingtransferred by magnetic or other propulsion uniformly over the area ofthe gaps between vanes 4 and 8.

Similarly, if slots 11 and 12 were not cut in vanes 4 of inner electrodeassembly 2, the outwardly disposed force acting upon the currentconduction paths would tend only to move the arc paths outwardly to thecorner edges of vanes 4 of arc-electrode assembly 2 and the arc wouldstay there, causing a destructive anode spot at high currents ratherthan migrate upwardly to cover the entire surface of vane 4. Once thedischarge is dispersed between electrode apparatus 2 and 4, as describedabove, no high current density electrode spots, particu- "larlydestructive anode spots, are formed, and the entire interior surface ofthe envelope within the arcing area is filled with a gaseous plasmaconducting electrically between the outwardly and inwardly disposedelectrode assemblies. Current continues to flow until the occurrence ofa first current zero, at which time the existing arcs are extinguishedand the vaporized metals, which constitute conduction carriers of thedischarge evaporate to the cold walls where they condense, so that thehigh dielectric strength of the vacuum is returned, holding off furtherhigh, but permissible voltages.

FIGURE 4 of the drawing illustrates, in vertical cross sectional view, amultiple-stage, cascaded, triggered vacuum gap device constructed inaccord with the present invention. The device of FIGURE 4 is animprovemen upon the multiple stage trigger vacuum gap device disclosedand claimed in my aforementioned copending application, Ser. No.586,751, filed Oct. 14, 1966 and includes an evacuable envelopeindicated generally as 35, including a pair of insulating cylindricalsidewall envelope members 36 and 37 disposed along a common axis andconnected by an annular ring electrode support member 38 by a pair ofannular flange ceramic-to-metal seals 39 and 40. The ends of evacuableenvelope 35 are closed by a pair of apertured cup members 41 and 42',each of which is fastened to the respective juxtaposed cylindricalinsulating body by an annular collar 43 and an annularmetallic-to-ceramic sealing flange 44. A trigger electrode assembly 45is disposed within the aperture in cup member 41 and hermetically sealedthereto. A trigger electrode assembly 46 is disposed within the aperturein end cup 42 and hermetically sealed thereto. A trigger electrode leadwire 47 is used to supply an electrical signal to trigger electrodeassembly 45 and a similar trigger electrode lead 48 supplies a signal totrigger electrode assembly 46. Each of trigger electrode leads 47 and 48is passed in insulating relationship through trigger electrode assembly45 or 46 through respective insulating bushings 49 and 40.

The members enclosed within that portion of envelope 35 generallyencompassed by cylindrical insulat ing member 36 constitutes a firsttriggerable gap stage represented generally by 60 and the membersenclosed within that portion of evacuable envelope 35 including thevolume encompassed by cylindrical insulating member 37 constitutes asecond triggerable gap assembly repre sented generally by 70. Firsttriggerable gap stage 60 includes an outer electrode assembly 61including a cylindrical outer member 62 and a plurality of relativelythin extended area inwardly-dependent radial fins 63 which are parallelwith the longitudinal axis of the device of FIGURE 4, which axis may bedescribed as a line passing through the central portions of triggerelectrode assemblies 45 and 46, about which the cylindrical insulatingmembers 36 and 37 are concentric. A second electrode assembly 64 withintriggerable gap stage 60 include a plurality of outwardly-dependingthin, relatively large area, radial vanes 65. Vanes 65 are disposed soas to be interposed between adjacent vanes 63 of electrode assembly 61and are equidistant from adjacent ones thereof. The length thereof isslightly less than the length of the inwardly dependent vanes 63 ofouter electrode assembly 61. The vanes 65 are each supplied with slots11 and 12, as is the device of FIGURE 1, for insuring that the electricdischarge paths within stage 60 are evenly dispersed over the entiresurface of the vanes, as in the device of FIGURE 1. Electrode assembly64 is mechanically and electrically connected to an annular supportmember 66 at the lower portions thereof, which annular support memberis, in turn, electrically and mechanically connected to and supported byannular member 38, which constitutes a portion of the evacuable envelope35. At the same point that annular support member 66 joins supportmember 38, support member 38 also is joined by a short cylindricalannular shield member 67, the prime purpose of which is to prevent thepassage of metallic particles out from the interelectrode space so as toshort-circuit the insulating cylinder 36 by causing the coating thereofwith metallic particles. Although this shield member is shown as beingrelatively short, it may be of any desired length and configurationsufficient to shield insulator 36 and to prevent an electric field fromoccurring in the area where 35 and 39 join.

The construction of the second triggerable vacuum gap stage of thedevice of FIGURE 4 represented generally by 70 is substantiallyidentical with that of the first stage 60 and like elements thereof areindicated by the corresponding numerals of the 70 series to thoseelements indicated in the 60 series in first triggerable gap stage 60 ofFIGURE 4. In first stage 60 of FIGURE 4, the inwardly-depending, outerradial vanes are shown in full and the outwardly-depending, inner radialvanes are shown in partial section. In stage 70', on the other hand, theinner outwardly-depending electrode vanes are shown in full view and theouter inwardly-depending vanes are shown in partial section. A plasmatransfer tube 80, which is a cylindrical member, is connected betweenthe inner electrode support members 66 and 76 and is electricallyconnected to the inner electrode assemblies 64 and 74. It presents anopen, unimpeded path for the conduction of electron-ion plasma betweenthe interaction spaces of stages 60 and 70 during operation.

Means are provided by contacts 81 and 82 to provide connection with anelectrical load circuit to be protected, switched, or otherwisecontrolled by the operation of the triggerable vacuum gap device ofFIGURE 4. A pair of capacitors 83 and 84 constituting a voltage dividernetwork having a center tap at 85, connected to electrode support member38, is connected between the load connectors 81 and 82. Means forapplying a triggering pulse to trigger electrode assemblies 45 and 46are provided by a pair of separate, but simultaneously controlled, pulsesources 86 which are connected to the associated trigger electrode lead49 or 50 and to cup members 41 and 42.

In FIGURE 4 the preferred structural materials of the variousillustrated constituents are substantially the same as the materials setforth with respect to the device of FIGURE 1. For example, members 36and 37 are a high voltage insulator, as for example, a fosteriteceramic, Pyrex glass, or high density alumina. Electrode assemblies 61,64 and 71 and members 66, 67 and 76 and 77 and 74 are made of extremelyhigh purity, preferably zone-refined material, as for example copperhaving less than 1 part 10 of gas, or gas-forming impurities,particularly oxygen or oxygen-containing impurities. Such material may,for example, be prepared in accord with the method set forth in US.Patent No. 3,234,351, issued Feb. 8, 1966 to M. H. Hebb. The othermetallic members, as for example, end cap members 43 and 44 and supportmember 38' should be constructed of high purity metals, as for example,copper, stainless steel, or nickel which are out-gassed to preclude thepresence of concentrations of gas or gas-forming materials, but need nothave the extremely high purity of the electrode materials themselves.Before operation, the device is evacuated to a pressure of 10 mm. ofmercury or less to obtain the high hold-01f and rapid recoverycharacteristics of vacuum.

In operation, it should be assumed that the device is to be used toswitch from a nonconducting to a conducing condition between a highvoltage applied between terminals 81 and 82. With the voltage suppliedbetween terminals 81 and 82, the voltage divider comprising capacitors83 and 84 causes a division of the applied voltage between the twoseries interelectrode gaps of stages 60' and 70. Thus, for example,approximately half the applied voltage is across the capacitor 83 andsimilarly, is applied across the vanes of electrode assemblies 61 and64. The remaining half of the applied voltage is across the capacitor 84and, similarly, is applied across the vanes of electrode assemblies 71and 74.

When it is desired to tire the device and to cause the voltage betweenterminals 81 an 82 to be short-circuited or switched, a predeterminedcontrol causes a positive pulse of from 50 to 5,000 volts, for example,depending upon the magnitude of the voltage being held off and thedimensions of the interelectrode gaps between the primary electrodeassemblies, to be applied to the trigger electrode leads 47 and 48respectively. If the applied line voltage is a unidirectional voltage,only one of the primary arc-electrodes 61 or 71 is associated with thetwo trigger assemblies 45 and 46 and will be negative. A positivetrigger voltage applied to the trigger associated 'with the negativeelectrode cause a trigger breakdown between that electrode assembly andthe trigger anode of the as sociated trigger assembly. If, on the otherhand, the voltage applied to terminals 81 and 82 is an alternatingvoltage, one of the two primary electrode assemblies 61 and 71 is morenegative than the other and the associated trigger assembly, either 45or 46, will break down, causing the injection of an electron-ion plasmainto the interelectrode space between the associated primary electrodes.Assuming the initial breakdown occurs in the interaction gap between theelectrode assemblies 61 and 64, a pulse of ion-electron plasma isinjected into the interelectrode spacing between electrodes assemblies61 and 64, causing the establishment of a high voltage are therebetween.Upon the establishment of the arc, the charge from capacitor -83discharges through the connections to the respective electrodes, thuspreventing the extinction of the arc and permitting the establishment ofa diffuse arc over the wide area of the narrow vanes 63 and 65 ofelectrode assemblies 61 and '64. Upon the establishment of the full arcacross the interelectrode gap between electrode assemblies 61 and 64,the electron-ion plasma generated thereby is propelled through arctransfer tube 80 and into the interelectrode spacing between the vanesof the electrodes of triggered gap sections 70, namely electrodeassemblies 71 and 74. With the establishment of the are between theelectrodes 61 and 64, substantially the entire voltage between theterminals 81 and '82 is transferred across capacitor 84. With this highvoltage applied across the electrodes 71 and 74 in the presence of theelectronion plasma propelled thereinto from triggered vacuum gap section60, an arc is established between electrode assemblies 71 and 74 withina matter of less than a microsecond after the initial breakdown of gapsection 60. Upon the establishment of an are between electrodeassemblies 71 and 74, the charge uopn capacitor 83 dischargesthereacross and the current is complete from terminals 81 through thespacing between electrode assemblies 61 and 64, then through the arebetween electrode assemblies 71 and 74 and finally, out to terminal 82,with the voltage distributed substantially evenly between the two arcsand the erosion upon any given arc-electrode being no greater than thatwould be if it were the only are between the arc terminals. As ismentioned hereinbefore, the erosion upon any given arc electrode isminimized or substantially eliminated by causing the slots in the inner,outwardlydisposed arc-electrode vanes to cause a folding-back of thecurrent conduction path with a resultant magnetic field which causes thearc currents to be diffused uniformly over the surfaces of therespective arc-electrode vanes rather than bunohing together at thecorners of the vanes and causing the establishment of a destructive anderoding anode footpoint thereat.

Also, in the operation of the device in accord with this embodiment ofthe present invention and the cascading of the plurality ofarc-electrodes and triggered vacuum gap stages, one upon another, it ispossible to hold off higher voltages because the ovltage held off isdistributed evenly as the number of gaps is increased, all withsubstantially no anode spot formation and erosion.

In FIGURE 5 of the drawing, an alternative arrangeelectrode assembly 74of FIGURE 6, wherein the horizontal slot 11 is at least two-thirds ofthe distance from the bottom of the vane 75. Although the folding-backof the current path described with respect to the devices of FIGURES l,3 and 4 which is accomplished by the configuration illustrated in FIGURE-6, is also achieved by the configuration illustrated in FIGURE 5, inpractice, on some devices which I have tested, it turns out that someerosion does occur when the vertical slotting is as in FIGURE 5. This isbecause the juxtaposition of the inwardly depending vanes 8 ofarc-electrode 4 of FIG- URE 1 terminates substantially evenly withvertical slot 12 in FIGURE 5, so that there is a tendency for an anodespot to form at the point where vertical slot 1-2 is cut. Accordingly,it has been determined experimentally, in devices constructed in accordwith the present invention which I have made, that the slotting shouldbe such that the vertical slot 12 does not intersect the plane of vane 4in a region that is closely disposed to the inward edge of inwardlydisposed vane 8 of arc-electrode assembly 4. Although in devices inaccord with the invention which I have constructed, this is achieved byslotting as in FIGURE 6, it is conceivable that in some otherdimensional relationships the vertical slot 12 in FIGURE 6 may, inanother configuration, be the one to be avoided. It sufiices to say thatthe vertical slot should be cut in the outwardy disposed vane so that itdoes not intersect the vane surface at a point that is closely disposedto the inward edge of inwardly disposed vanes 8 of arc-electrodeassembly 4.

The slotting of the vanes illustrated heretofor is entirely suitable toavoid the formation of anode spots in accord with the present invention.This is particularly so, irrespective of the material from which thearc-electrodes are fabricated. In particular, no further measures needbe taken if the arc-electrodes are fabricated from an alloy that has aparticularly high strength, as for example copper with minor additionsof beryllium, nickel, tin or lead. It should be appreciated, however,that the same magnetic forces that cause the arcing paths to be movedaround the corner of the inner, outwardly-disposed vanes, to avoid theformation of an anode spot upon the outer corner of the vane, also causeenormous forces to be exerted upon the vanes themselves. Although theaforementioned copper alloys and other high strength materials aresufficiently rigid and resilient to Withstand this force, particularlyif the slotting does not extend too deeply or too highly into the vane,as for example as illustrated in FIGURE 5, no deleterious etfect isnoted, If, however, the electrodes are fabricated of high purity copperor high purity tin or any such element which is relatively soft and isin a relatively pure state, or any alloy which is relatively soft, andif the slotting is such as to substantially weaken the mechanicalstrength of the vane, the mechanical forces caused by the magneticfields, due to the folding-back of the current path through the vanes,may tend to cause the portion of the =vane which is surrounded by thehorizontal and vertical slots to warp outwardly, away from the main bodyof the vane. It is desirable that such warping be avoided if such aductile material is utilized and the slotting is such as tosubstantially weaken it.

In FIGURE 7 of the drawing a central electrode assembly is illustratedwhich overcomes the aforementioned difficulty. In FIGURE 7, it may benoted that horizontal slot 11 does not extend to the edge of the vane 4but, rather, extends to within approximately thereof. In other respects,the configuration of the slots in the vane 4 of FIGURE 7 issubstantially the same as that illustrated in FIGURE 6. It has beenfound that the main path of current utilizing the vane slotconfiguration illustrated in FIGURE 7 does not substantially differ fromthat utilizing the vane slot configuration of FIGURE 5. This is becausethe conduction path from the lower to the upper portion of the vanethrough the narrow region 1 1 that is unslotted between the end ofhorizontal slot 11 and the edge of the vane is so small thatsubstantially no current, as compared with the current path in thefoldedback pattern, exist, so as to adversely affect the magneticcontrol of the current paths in accord with the present invention.

FIGURE 8 illustrates an alternative vane slot configuration to thatillustrated in FIGURE 7 which accomplishes the same purpose. In caseswhere it has been determined that passage of current through the uncutportion of the vanes is excessive or, for fabrication purposes when itis desired that it is most expedient and economical from themanufacturing point of view to cut the slot with a device such as aband-saw, the slots are cut as in FIGURE and a hole 90 is bored throughthe upper end of the plate 5 downwardly through vane 4 and through theslot. A small stainless steel pin 91 having a reduced area portion 92therein is placed into the hole with the reduced area portion 92adjacent the slot and not in contact with the vane thereat. Becausestainless steel is exceedingly strong and a very poor conductor ofelectric currents, the illustrated stainless steel pin in FIGURE 8 ofthe drawing is sufficient to withstand the magnetic forces tending tomove the slotted portion of the vane outwardly under magnetic stress,and yet is not such as to cause any change in the electric current pathwithin the vane, so that the vane operates substantially as thatillustrated in FIGURE 6 of the drawing, but without any distortion dueto the magnetic field and its effect upon the vane. Instead of stainlesssteel, any poor conductor or insulator which has sufficient strength maybe used.

FIGURE 9 of the drawing illustrates an alternative slotting, wherein theslot is cut in the form of a gentle curve which may be advisable from amanufacturing standpoint since a single cut with a band-saw mayaccomplish this fabrication. Functionally, the slot pattern illustratedin FIGURE 9 of the drawing is the substantial equivalent of that shownin FIGURES 5 and 6. Since, however, the same forces which operate onthese vanes may tend to force the remote portion of the vane outwardlyduring arcing if the material is soft, it may be advisable to utilizethe same technique in FIGURE 9 as is illustrated in FIGURE 8, drilling ahole through plate 5 into vane 4 and inserting a suitable stainlesssteel or other high-strength, poorly electrical conductive material tokeep the vane from being distorted.

FIGURE of the drawing illustrates yet another alternative embodiment ofthe invention. In FIGURE 10, a vacuum switch embodying the inventionoperates to move from a circuit-making to a circuit-breaking position inresponse to a rotational motion of the central electrode assembly. Theenvelope of the device of FIGURE 10 is composed of a substantiallycylindrical, metallic side wall member 100, an upper closed end plate101 and a lower, dished, or upwardly flanged, apertured end plate 102.Member 100 is composed of a highly conductive material, as for example,copper. Members 101 and 102 are composed of a suitable gas imperviousinsulating dielectric material as for example, an alumina ceramic.Apertured end wall member 102 is fastened hermetically to cylindricalside wall member 100 by means of an annular sealing flange 103,preferably of a fernico alloy. A vacuum-tight sleeve bearing104permitting limited rotation of the central electrode assembly isconnected and hermetically sealed with central electrode support rod 105and comprises a sleeve member 106 which is hermetically sealed toceramic end Wall member 102 by means of an annular ceramic-to-metalsealing flange member 107. Electrical contact is made to the respectiveprimary electrode apparatus by making contacts to electrode supportmember 105, as represented schematically by arrow 108, and by makingcontact to cylindrical side wall member 100 at terminal lug 109, asrepresented schematically by arrow 110. An alternating current source111 and a suitable load impedance 112 may be disposed in series orparallel circuit relationship between these points, as indicatedschematically.

In operation, the device, once having been fabricated and evacuated. toa pressure of less than 10* mm. of mercury, is caused to move from acircuit-making condition in which the electrodes are in substantialmating position to a circuit-breaking position, by a slight rotation ofthe central electrode apparatus. Contact is made between coupled thincontact vanes each of which is substantially perpendicular to the sametransverse plane at the abutting edges thereof. To increase the area ofcontact, both inner and outer vanes are beveled at the ends to meetfiushly with the mating vane. It is along these beveled surfaces that aplurality of parallel arcs are struck upon separation of the electrodes.As the arc current increases the discharge spreads out substantiallyover the entire surface of the vanes constituting the individualportions of the electrode structure. Since the arc is extinguished atthe first occurring current zero, which for 60 cycle alternating currentoccurs at less than 8 milliseconds, the vanes do not have time toseparate far enough so that the arc spreads between the back surface ofa movable vane and the back surface of the next adjacent fixed vane.Hence, arcs are established in the switch only between mating vaneswhich are separated by the circuit breaking rotation. Arcs are notgenerated at the other gaps due to the simple fact that it is notmechanically feasible to bring the remaining gaps to the gap lengthrequired to strike arcs therein less than 8 milliseconds.

As in the devices illustrated in FIGURES l through 9, slots 11 and 12 inthe outwardly projecting vanes of the inner electrode assembly causemagnetic forces to move the arcs over the entire surfaces of therespective vanes, preventing the formation of destructive anode spots.

From the foregoing it should be readily apparent that, in accord withthe present invention, I provide improved vacuum gap devices, such astriggerable vacuum gap and vacuum switch devices, having a pair ofarc-electrodes in which a first inner electrode has a plurality ofoutwardly-disposed electrode vanes and a second outer electrode withinwardly-disposed electrodes vanes which avoid the formation of anodespots. In accord with the present invention, anode spot formation isavoided by causing the vanes of the inner electrode assembly to beappropriately slotted, thus causing currents therein to be folded-back,causing magnetic flux lines to force current conduction paths to diffuseevenly over a large area of the electrode vanes. This diffusion over alarge area keeps the current density to a relatively low value andprevents the current from exceeding the threshold for the formation ofanode spots. Devices constructed in accord with the present inventionmay, therefore, carry much higher currents, without destructive erosionthereof, than such devices which do not have this improved geometry.

While the invention has been described hereinbefore with respect tocertain embodiments and features thereof, many modifications and changeswill readily occur to those skilled in the art. Accordingly, it isintended by the appended claims to cover all such modifications andchanges as fall within the true spirit and scope of the invention. Thusfor example, although throughout the description the inner electrodeassembly has been described as being slotted, advantageous results maybe obtained by slotting the outer electrodes, using the same criteria,instead. Alternatively, both electrode assemblies may be slotted. Theimportant criterion is that at least one electrode assembly be slottedto cause a folding-back of current paths and a magnetic field todisperse current paths over the electrode vane area. For ease offabrication and superior performance, however, I prefer to slot theinner electrode assembly vanes only.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A vacuum gap discharge device comprising:

(a) an hermetically sealed envelope evacuated to a 13 pressure of 10-mm. of Hg or less and including a portion fabricated from a high voltagedielectric;

(b) a first primary arc-electrode assembly supported within saidenvelope and including a first plurality of thin substantially planarvanes projecting therefrom and being substantially perpendicular to atransverse plane through said envelope;

(c) a second primary arc-electrode assembly supported within saidenvelope and including a second plurality of thin substantially planarvanes projecting therefrom and being substantially perpendicular to saidtransverse plane through said envelope;

((1) the vanes of said first primary arc-electrode assembly and thevanes of said second primary arcelectrode assembly being interleavedalternatively between one another so as to define a plurality ofelectrically-parallel gaps between said first and second primaryarc-electrode assemblies to cause electrical breakdown between saidprimary arc-electrode assemblies to occur simultaneously at amultiplicity of points whereby the formation of high current densityanode spots is avoided;

(d1) the vanes of at least one of said electrode assemblies having slotscut therein from passing radially therein over a substantial portionthereof but requiring current paths from the edges of a major portion ofthe edges thereof to describe a folded-back path creating magneticfields which force a diffusion of arcing currents over a large surfaceportion of said vanes,

(e) means for connecting said primary arc-electrode assemblies incircuit with a high power electric line; and

(f) means for producing at a preselected time a copious quantity ofelectron-ion plasma within said electrically-parallel gaps to establisha plurality of electrically-parallel current arcs within said envelopewhereby said device carries a high power load without destructiveformation of anode spots on said electrodes.

2. The device of claim 1 wherein said slots in the vanes are cut in saidinner electrode assembly.

3. The device of claim 1 wherein the slots are cut in both inner andouter electrode assemblies.

4. The device of claim 1 wherein said slots comprise a first slotsubstantially perpendicular to the longitudinal axis of said device andat least approximately two-thirds of the distance from the end of saidassembly at which said electron-ion plasma is first produced and asecond slot which is substantially parallel with the longitudinal axisof said device and intersects said first slot.

5. The device of claim 1 wherein said slots comprise a first slotsubstantially perpendicular to the longitudinal axis of said device anda second slot substantially parallel to the longitudinal axis of saiddevice, intersecting said first slot, and disposed at a distance of atleast approximately two-thirds of the distance from the active edgethereof which is closest to said other electrode assembly.

6. The device of claim 1 wherein said slots comprise the slotconfiguration set forth in claims 4 and 5.

7. The device of claim 1 wherein the device is a fixed gap device withstationary electrode assemblies and the means for supplying said plasmais a trigger electrode assembly which is operative to an externalelectrical pulse to inititate breakdown.

8. The device of claim 1 wherein the device is a vacuum switch with atleast one electrode assembly movable in response to an external force toseparate the vanes of said electrode assemblies, said separating of saidvanes constituting means for establishing an electron-ion plasma betweensaid arc-electrode assemblies.

9. The device of claim 2 wherein said slots comprise a first slotsubstantially perpendicular to the longitudinal axis of said device andat least approximately two-thirds the length of said vanes from the endthereof at which said plasma first appears and said second slot issubstantially parallel to the axis of said device and at leastapproximately two-thirds the width of said vanes from the edge thereofwhich is closest to said outer arc-electrode assembly and intersectssaid first slot.

10. The device of claim 9 wherein said first slot does not extendentirely to the edge of said vane, but is terminated at a distancetherefrom which is sufficient to leave a quantity of said vane betweenportions thereof on either side of said slot which is mechanicallystrong enough to prevent deformation of said vane due to concentratedmagnetic forces but which is narrow enough so as to have negligibleelfect upon said folded-back current paths within said vane.

11. The device of claim 9 wherein said first slot extends to the edge ofsaid vane and a bore is made through said vane passing through said slotand substantially parallel to the longitudinal axis of said device and apin having high strength, but poor electrical conductivity is insertedtherein bridging said slot and preventing deformation of said vaneduring operation by magnetic forces.

12. The device of claim 11 wherein said pin is stainless steel and saidelectrode is high purity copper.

References Cited UNITED STATES PATENTS 2,896,104 7/ 1959 Sedlacek 3l3217X JAMES W. LAWRENCE, Primary Examiner.

R. F. HOSSFELD, Assistant Examiner.

US. Cl. X.R. 313-217; 315-11l 22 33 UNITED STATES PATENT OFFICECERTlFlCATE OF CORRECTION Patent No. 3L432 ]13 Dated March 11, 1969Inventor(s) James M, Laffertv It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 13, line 24, after "therein", insert preventing current pathstherein SIGNED AND SEALED MAR 101970 (SEAL) Attest:

Edward M. Fletcher, Jr. LL AM E. SGHUYLER JR.

Allowing Officer Commissioner of Patents

